The present invention relates generally to oil seals, and in particular, to the manufacture of a one-piece oil seal that includes a principal lip and an auxiliary, opposite-facing lip, and also includes a separate nylon or like, anti-extrusion insert.
Particularly in the field of power steering seals, namely, those which act in cooperation with highly pressurized mechanisms including a steering rack, it is essential to obtain the best performance at lowest cost. Many years ago, it was discovered that the use of a bonded rubber oil seal could be backed up with an insert, preferably a nylon insert, to withstand the relatively high pressures found in power steering mechanisms at the time. Thus, with such seals undergoing sliding motion or both rotary and sliding motion, there was the strong possibility that dirt or other contaminations would enter and be moved along the steering rack, eventually scoring the rack or the seal and leading to leakage.
However, at that time, the oil seal was fitted with one or more separately formed back-up components, including those which contained auxiliary lips, all of which served to exclude contaminants from under the lip seal.
Because the cost of the seal is almost low in respect to the cost of labor to replace it, it is most important that seals provide a great deal of reliability when installed. Consequently, a number of designs have been selected and used, including those shown in U.S. Pat. No. 5,456,475. In this seal, the nylon insert is formed as a part of the back-up ring and the entire unit is much larger than necessary. It in turn is then backed up by a still further separately formed auxiliary or dirt lip with its own casing and rubber mounting diameter. In this design, therefore, the nylon back-up ring is somewhat reluctant to "float" and hence, to follow the shaft as closely as might be desired, although it is extrusion-proof.
Another approach has been to offset the inner part of the radial flange of the casing, thereby imparting a stepped appearance to it. With this configuration, the rubber can flow into the cavity thus formed, and surround the insert and thus add stability to the seal. However, such seals are capable of still further improvement, particularly those which are exposed to very high pressures and the possibility of allowing contaminants to enter them from the air side of the seal.
In view of the need for a further improved seal of the foregoing type for use in high pressure applications, it is an object of the present invention to provide an improved high pressure resistant seal.
Another object of the invention is to provide a method which makes it possible to use a more flexible type of nylon insert than has been previously indicated.
Yet another object of the invention is to provide a seal which can be made economically and with virtually the same cost as prior art seals yet provide improved performance in use.
Still another object of the invention is to provide a composite seal which is easy to manufacture and which will provide a high degree of reliability and use.
A further object of the invention is to provide a seal which may be optionally used with a simply formed seal providing a bonded dirt lip as well as an extra dirt lip, if necessary.
A still further object of the invention is to provide a seal which will resist high pressures in the application, and which includes plural ribs on the air side of the sealing lip and an integral dirt lip bonded to the casing.
An additional object of the invention is to provide a dirt lip containing a contoured inner diameter on the casing or stamping of the seal.
A still further object of the invention is to provide a seal with a stamping which can lie close to the shaft being sealed without unduly compromising the bonding of the seal dirt lip to the casing.
A further object of the invention is to provide a novel method of making a seal according to the invention.
A still further object of the invention is to provide a method wherein the rubber forming the bond between itself and the casing may flow readily into the necessary areas.